The objects are, for example, mines laid on the seabed. For this application, the sonars comprise an emission antenna emitting an acoustic beam directed toward the seabed covering a useful angular sector starting from the antenna and delimited by two directions inclined with respect to the horizontal and to the vertical. The useful angular sector delimits the zone of the seabed that the sonar is intended to image. Stated otherwise, the sonar is intended to image the seabed zone intercepted by the angular sector.
These sonars are usually mounted on a submersible carrier such as a towed or autonomous underwater craft or under the hull of a surface vessel.
Contemporary emitting antennas are cylindrical antennas or plane antennas. These antennas exhibit an emission pattern comprising a main lobe and sidelobes, the emission pattern being symmetric with respect to the maximum of the main lobe. For example, plane antennas exhibit a sin x/x emission pattern. The antennas are usually configured in such a way that the maximum of energy is emitted between the first and the second direction, that is to say within the useful angular sector.
These antennas consume significant energy. Now, mine hunting is steering toward autonomous craft for the search for mines. A significant point in the performance of a sonar embedded aboard an autonomous craft is its low energy consumption.
It is noted moreover that these antennas exhibit limited performance by creating multiple paths toward the surface, notably in shallow waters (typically less than 30 m).